I have a CT33 coming to me on loan (along with a calibration plate), so I will get to see for myself how well it works.
The benefit of the General Tools device is not so much its low cost, but the "hold" button and audio feedback it gives when trying to locate a peak. Among the several things I want to check out on one of the boats, there is one spot that is not in my line of sight. So the option to reach around a corner, locate the peak via audio feedback, press the hold button, and then look at the reading sounds very useful. But I would need to try it to see if this procedure actually works as well as it sounds.
I may buy the General Tools one from a place with a liberal return policy to compare them side-by-side. Then I'll do some comparisons with the calibration plate and various spacers (to test the effect of the different reported depth sensitivities) as well as some readings on different parts of my two current boats, and see if the two correlate close enough. Hopefully, with the 10 different material calibrations, there will be one that approximates the readings close enough. Like I said, the main interest is in looking for relative gradients to trace the source of leaks. I also realize that there are a whole lot of factors that can lead to false positives and false negatives, regardless of what brand of meter you use.